The present invention relates to an improved tensioning structure for a sliding closure unit. More particularly, the present invention is directed to an improved sliding closure unit for controlling the discharge of molten metal from a metallurgical vessel and of the type including a stationary refractory plate to be mounted on the metallurgical vessel with a discharge opening aligned with the discharge nozzle of the metallurgical vessel, a movable refractory plate having a discharge opening, a slide frame supporting the movable refractory plate and movable in a direction of movement between an open position with the discharge openings of the movable and stationary refractory plates in alignment and a closed position with the discharge plates out of alignment, and tensioning means for sealingly pressing the movable refractory plate against the stationary refractory plate, whereby surfaces of the movable refractory plate extending in the direction of movement on opposite sides of the discharge openings are loaded by the tensioning means on the underside of the movable refractory plate, as a result of which the movable refractory plate is pressed toward the stationary refractory plate.
A sliding closure unit of this general type is disclosed in DE-OS No. 21 46 677 and includes two movable refractory plates guided in guide elements and inserted one behind the other in the direction of movement. One movable refractory plate is positioned beneath the discharge nozzle and is pressed by tensioning means against the stationary refractory plate. The tensioning means consists of pivotally mounted levers which pivot about a stationary horizontal axle and pressure springs located in the guide elements. The levers are positioned to extend transverse to the direction of movement. The springs contact first ends of the levers and urge the levers to pivot about the axles and to urge second ends of the levers directly into contact with the movable refractory plate, thereby urging the movable refractory plate toward the stationary refractory plate. A metal shell surrounds the sides and bottom of the movable refractory plate and normally is formed of a soft steel material. The second ends of the levers thereby slidingly contact the bottom of such metal shell. In this arrangement, the levers thereby contact the metal shell at substantially concentrated points, and this creates pressure peaks which have an undesirable effect over the course of the life of the movable refractory plate, which, as is known, is subjected to great wear otherwise during use due to the development of large amounts of heat.
Additionally, development in this technology is to avoid the use of a metal shell having a bottom portion and to simply surround the circumference of the movable refractory plate by a hoop or band of metal. In such an arrangement, the levers would be pressed directly against the hard brittle refractory material of the movable refractory plate, thereby producing in the plate impressions and even cracks.